This behavior appears to have changed, with weird results in https://nl.wikipedia.org/w/index.php?title=Overleg_Wikipedia:Universele_gedragscode&type=revision&diff=56535077&oldid=56534101
It hasn't changed but I should've clarified in the original report that this only affects replies which are new at that level. In the diff you gave there was already a reply at that level (2.1), so (2.2) was just appending to an existing numbered list.
Replying to a nested numbered list, see https://nl.wikipedia.org/w/index.php?title=Overleg_Wikipedia:Universele_gedragscode&type=revision&diff=56535077&oldid=56534101&diffmode=source . That is a list with two levels. With my edit I added a numbered point on the second level, that is now point 2 within outer level point 2. Now when you hit reply to that point, the text box appears right beneath it and indented with a bullet. However when you hit reply to the point above, point 1 within outer level point 2 it is going to be point 6 on the outer level. This is because points 1 and 2 of the outer level haven't been signed, I assume. However, it feels really weird.